Effects of cholecystokinin (CCK) and other secretagogues on isoforms of protein kinase C (PKC) in pancreatic acini

Docosahexaenoic Acid Inhibits Expression of Fibrotic Mediators in Mice With Chronic Pancreatitis

Background

Chronic pancreatitis (CP) is an irreversible progressive disease that destroys exocrine parenchyma, which are replaced by fibrous tissue. As pancreatic fibrosis is a key feature of CP, reducing fibrotic protein content in the pancreas is crucial for preventing CP. Studies suggest that NF-κB facilitates the expression of fibrotic mediators in pancreas and protein kinase C-δ (PKC-δ) regulates NF-κB activation in stimulated pancreatic acinar cells. Docosahexaenoic acid (DHA) is an omega-3 fatty acid having anti-inflammatory and anti-fibrotic effects. It has been shown to inhibit NF-κB activity in cerulein-stimulated pancreatic acinar cells which is a cellular model of CP. In the present study, we investigated if DHA inhibits expression of fibrotic mediators by reducing PKC-δ and NF-κB expression in mouse pancreatic tissues with CP.

Methods

For six weeks, mice were weekly induced for acute pancreatitis to develop CP. Furthermore, acute pancreatitis was induced by hourly intraperitoneal injections of cerulein (50 μg/kg × 7). Mice were administered DHA (10 μM) via drinking water before and after CP induction.

Results

Cerulein-induced pancreatic damages like decreased pancreatic weight/total body weight, leukocyte infiltration, necrosis of acinar cells, and vacuolization were found to be inhibited by DHA. Additionally, DHA inhibited cerulein-induced fibrotic mediators like alpha-smooth muscle actin and fibronectin in pancreas. DHA reduced expression of PKC-δ and NF-κB p65 in pancreatic tissues of cerulein-treated mice.

Conclusions

DHA may be beneficial in preventing CP by suppressing pancreatic expression of fibrotic mediators.

Protein kinase C isoforms in the normal pancreas and in pancreatic disease

Protein Kinase C isoforms have been implicated in regulating multiple processes within the healthy pancreas. Moreover, their dysregulation contributes to all aspects of pancreatic disease. In this review, with a focus on acinar, ductal, and islet cells, we highlight the roles and contributions of the different PKC isoforms to normal pancreas function. We also discuss the contribution of PKC enzymes to pancreatic diseases, including insulin resistance and diabetes mellitus, as well as pancreatitis and the development and progression of pancreatic cancer.

Docosahexaenoic Acid Inhibits Cerulein-Induced Acute Pancreatitis in Rats

Oxidative stress is an important regulator in the pathogenesis of acute pancreatitis (AP). Reactive oxygen species induce activation of inflammatory cascades, inflammatory cell recruitment, and tissue damage. NF-κB regulates inflammatory cytokine gene expression, which induces an acute, edematous form of pancreatitis. Protein kinase C δ (PKCδ) activates NF-κB as shown in a mouse model of cerulein-induced AP. Docosahexaenoic acid (DHA), an ω-3 fatty acid, exerts anti-inflammatory and antioxidant effects in various cells and tissues. This study investigated whether DHA inhibits cerulein-induced AP in rats by assessing pancreatic edema, myeloperoxidase activity, levels of lipid peroxide and IL-6, activation of NF-κB and PKCδ, and by histologic observation. AP was induced by intraperitoneal injection (i.p.) of cerulein (50 μg/kg) every hour for 7 h. DHA (13 mg/kg) was administered i.p. for three days before AP induction. Pretreatment with DHA reduced cerulein-induced activation of NF-κB, PKCδ, and IL-6 in pancreatic tissues of rats. DHA suppressed pancreatic edema and decreased the abundance of lipid peroxide, myeloperoxidase activity, and inflammatory cell infiltration into the pancreatic tissues of cerulein-stimulated rats. Therefore, DHA may help prevent the development of pancreatitis by suppressing the activation of NF-κB and PKCδ, expression of IL-6, and oxidative damage to the pancreas.

NF-κB in acute pancreatitis: Mechanisms and therapeutic potential

The incidence of acute pancreatitis (AP) is increasing globally and mortality could be high among patients with organ failure and infected necrosis. The predominant factors responsible for the morbidity and mortality of AP are systemic inflammatory response syndrome and multiorgan dysfunction. Even though preclinical studies have shown antisecretory agents (somatostatin), antioxidants (S-adenosyl methionine [SAM], selenium), protease inhibitors, platelet activating factor inhibitor (Lexipafant), and anti-inflammatory immunomodulators (eg. prostaglandin E, indomethacin) to benefit AP in terms of reducing the severity and/or mortality, most of these agents have shown heterogeneous results in clinical studies. Several years of experimental studies have implicated nuclear factor-kappa B (NF-κB) activation as an early and central event in the progression of inflammation in AP. In this manuscript, we review the literature on the role of NF-κB in the pathogenesis of AP, its early intraacinar activation, and how it results in progression of the disease. We also discuss why anti-protease, antisecretory, and anti-inflammatory agents are unlikely to be effective in clinical acute pancreatitis. NF-κB, being a central molecule that links the initial acinar injury to systemic inflammation and perpetuate the inflammation, we propose that more studies be focussed towards targeted inhibition of NF-κB activity. Direct NF-κB inhibition strategies have already been attempted in patients with various cancers. So far, peroxisome proliferator activator receptor gamma (PPAR-γ) ligand, pyrrolidine dithiocarbamate (PDTC), proteasome inhibitor and calpain I inhibitor have been shown to have direct inhibitory effects on NF-κB activation in experimental AP.

Involvement of myristoylated alanine-rich C kinase substrate phosphorylation and translocation in cholecystokinin-induced amylase release in rat pancreatic acini

Cholecystokinin (CCK) is a gastrointestinal hormone that induces exocytotic amylase release in pancreatic acinar cells. The activation of protein kinase C (PKC) is involved in the CCK-induced pancreatic amylase release. Myristoylated alanine-rich C kinase substrate (MARCKS) is a ubiquitously expressed substrate of PKC. MARCKS has been implicated in membrane trafficking in several cell types. The phosphorylation of MARCKS by PKC results in the translocation of MARCKS from the membrane to the cytosol. Here, we studied the involvement of MARCKS in the CCK-induced amylase release in rat pancreatic acini. Employing Western blotting, we detected MARCKS protein in the rat pancreatic acini. CCK induced MARCKS phosphorylation. A PKC-δ inhibitor, rottlerin, inhibited the CCK-induced MARCKS phosphorylation and amylase release. In the translocation assay, we also observed CCK-induced PKC-δ activation. An immunohistochemistry study showed that CCK induced MARCKS translocation from the membrane to the cytosol. When acini were lysed by a detergent, Triton X-100, CCK partially induced displacement of the MARCKS from the GM1a-rich detergent-resistant membrane fractions (DRMs) in which Syntaxin2 is distributed. A MARCKS-related peptide inhibited the CCK-induced amylase release. These findings suggest that MARCKS phosphorylation by PKC-δ and then MARCKS translocation from the GM1a-rich DRMs to the cytosol are involved in the CCK-induced amylase release in pancreatic acinar cells.

Acute pancreatitis: The stress factor

Acute pancreatitis is an inflammatory disorder of the pancreas that may cause life-threatening complications. Etiologies of pancreatitis vary, with gallstones accounting for the majority of all cases, followed by alcohol. Other causes of pancreatitis include trauma, ischemia, mechanical obstruction, infections, autoimmune, hereditary, and drugs. The main events occurring in the pancreatic acinar cell that initiate and propagate acute pancreatitis include inhibition of secretion, intracellular activation of proteases, and generation of inflammatory mediators. Small cytokines known as chemokines are released from damaged pancreatic cells and attract inflammatory cells, whose systemic action ultimately determined the severity of the disease. Indeed, severe forms of pancreatitis may result in systemic inflammatory response syndrome and multiorgan dysfunction syndrome, characterized by a progressive physiologic failure of several interdependent organ systems. Stress occurs when homeostasis is threatened, and stressors can include physical or mental forces, or combinations of both. Depending on the timing and duration, stress can result in beneficial or harmful consequences. While it is well established that a previous acute-short-term stress decreases the severity of experimentally-induced pancreatitis, the worsening effects of chronic stress on the exocrine pancreas have received relatively little attention. This review will focus on the influence of both prior acute-short-term and chronic stress in acute pancreatitis.

Pancreatic acinar cell nuclear factor κB activation because of bile acid exposure is dependent on calcineurin

Biliary pancreatitis is the most common etiology of acute pancreatitis, accounting for 30-60% of cases. A dominant theory for the development of biliary pancreatitis is the reflux of bile into the pancreatic duct and subsequent exposure to pancreatic acinar cells. Bile acids are known to induce aberrant Ca(2+) signals in acinar cells as well as nuclear translocation of NF-κB. In this study, we examined the role of the downstream Ca(2+) target calcineurin on NF-κB translocation. Freshly isolated mouse acinar cells were infected for 24 h with an adenovirus expressing an NF-κB luciferase reporter. The bile acid taurolithocholic acid-3-sulfate caused NF-κB activation at concentrations (500 μm) that were associated with cell injury. We show that the NF-κB inhibitor Bay 11-7082 (1 μm) blocked translocation and injury. Pretreatment with the Ca(2+) chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, the calcineurin inhibitors FK506 and cyclosporine A, or use of acinar cells from calcineurin Aβ-deficient mice each led to reduced NF-κB activation with taurolithocholic acid-3-sulfate. Importantly, these manipulations did not affect LPS-induced NF-κB activation. A critical upstream regulator of NF-κB activation is protein kinase C, which translocates to the membranes of various organelles in the active state. We demonstrate that pharmacologic and genetic inhibition of calcineurin blocks translocation of the PKC-δ isoform. In summary, bile-induced NF-κB activation and acinar cell injury are mediated by calcineurin, and a mechanism for this important early inflammatory response appears to be upstream at the level of PKC translocation.

PKCθ activation in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters and growth factors is needed for stimulation of numerous important cellular signaling cascades

The novel PKCθ isoform is highly expressed in T-cells, brain and skeletal muscle and originally thought to have a restricted distribution. It has been extensively studied in T-cells and shown to be important for apoptosis, T-cell activation and proliferation. Recent studies showed its presence in other tissues and importance in insulin signaling, lung surfactant secretion, intestinal barrier permeability, platelet and mast-cell functions. However, little information is available for PKCθ activation by gastrointestinal (GI) hormones/neurotransmitters and growth factors. In the present study we used rat pancreatic acinar cells to explore their ability to activate PKCθ and the possible interactions with important cellular mediators of their actions. Particular attention was paid to cholecystokinin (CCK), a physiological regulator of pancreatic function and important in pathological processes affecting acinar function, like pancreatitis. PKCθ-protein/mRNA was present in the pancreatic acini, and T538-PKCθ phosphorylation/activation was stimulated only by hormones/neurotransmitters activating phospholipase C. PKCθ was activated in time- and dose-related manner by CCK, mediated 30% by high-affinity CCK(A)-receptor activation. CCK stimulated PKCθ translocation from cytosol to membrane. PKCθ inhibition (by pseudostrate-inhibitor or dominant negative) inhibited CCK- and TPA-stimulation of PKD, Src, RafC, PYK2, p125(FAK) and IKKα/β, but not basal/stimulated enzyme secretion. Also CCK- and TPA-induced PKCθ activation produced an increment in PKCθ's direct association with AKT, RafA, RafC and Lyn. These results show for the first time the PKCθ presence in pancreatic acinar cells, its activation by some GI hormones/neurotransmitters and involvement in important cell signaling pathways mediating physiological responses (enzyme secretion, proliferation, apoptosis, cytokine expression, and pathological responses like pancreatitis and cancer growth).

Chronic stress sensitizes rats to pancreatitis induced by cerulein: Role of TNF-α

AIM: To investigate chronic stress as a susceptibility factor for developing pancreatitis, as well as tumor necrosis factor-α (TNF-α) as a putative sensitizer.

METHODS: Rat pancreatic acini were used to analyze the influence of TNF-α on submaximal (50 pmol/L) cholecystokinin (CCK) stimulation. Chronic restraint (4 h every day for 21 d) was used to evaluate the effects of submaximal (0.2 μg/kg per hour) cerulein stimulation on chronically stressed rats.

RESULTS: In vitro exposure of pancreatic acini to TNF-α disorganized the actin cytoskeleton. This was further increased by TNF-α/CCK treatment, which additionally reduced amylase secretion, and increased trypsin and nuclear factor-κB activities in a protein-kinase-C δ and ε-dependent manner. TNF-α/CCK also enhanced caspases’ activity and lactate dehydrogenase release, induced ATP loss, and augmented the ADP/ATP ratio. In vivo, rats under chronic restraint exhibited elevated serum and pancreatic TNF-α levels. Serum, pancreatic, and lung inflammatory parameters, as well as caspases’activity in pancreatic and lung tissue, were substantially enhanced in stressed/cerulein-treated rats, which also experienced tissues’ ATP loss and greater ADP/ATP ratios. Histological examination revealed that stressed/cerulein-treated animals developed abundant pancreatic and lung edema, hemorrhage and leukocyte infiltrate, and pancreatic necrosis. Pancreatitis severity was greatly decreased by treating animals with an anti-TNF-α-antibody, which diminished all inflammatory parameters, histopathological scores, and apoptotic/necrotic markers in stressed/cerulein-treated rats.

CONCLUSION: In rats, chronic stress increases susceptibility for developing pancreatitis, which involves TNF-α sensitization of pancreatic acinar cells to undergo injury by physiological cerulein stimulation.

Protein kinase C delta-mediated processes in cholecystokinin-8-stimulated pancreatic acini

OBJECTIVES

To define the role of protein kinase C delta (PKC delta) in acinar cell responses to the hormone cholecystokinin-8 (CCK) using isoform-specific inhibitors and a previously unreported genetic deletion model.

METHODS

Pancreatic acinar cells were isolated from (1) rat, and pretreated with a PKC delta-specific inhibitor or (2) PKC delta-deficient and wild type mice. Isolated cells were stimulated with CCK (0.001-100 nmol/L) and cell responses were measured.

RESULTS

The PKC delta inhibitor did not affect stimulated amylase secretion from rat pancreatic acinar cells. Cholecystokinin-8 stimulation induced a typical biphasic dose-response curve for amylase secretion in acinar cells isolated from both PKC delta(-/-) and wild type mice, with maximal stimulation at 10-pmol/L CCK. Cholecystokinin-8 (100 nmol/L) induced zymogen and nuclear factor kappaB activation in both PKC delta(-/-) and wild type mice, although it was up to 50% less in PKC delta(-/-).

CONCLUSIONS

In contrast to previous studies, this study has used specific and complementary approaches to examine PKC delta-mediated acinar cell responses. We could not confirm that it mediates amylase release but corroborated its role in the early stages of acute pancreatitis.

Gastrointestinal growth factors and hormones have divergent effects on Akt activation

Akt is a central regulator of apoptosis, cell growth and survival. Growth factors and some G-protein-coupled receptors (GPCR) regulate Akt. Whereas growth-factor activation of Akt has been extensively studied, the regulation of Akt by GPCR's, especially gastrointestinal hormones/neurotransmitters, remains unclear. To address this area, in this study the effects of GI growth factors and hormones/neurotransmitters were investigated in rat pancreatic acinar cells which are high responsive to these agents. Pancreatic acini expressed Akt and 5 of 7 known pancreatic growth-factors stimulate Akt phosphorylation (T308, S473) and translocation. These effects are mediated by p85 phosphorylation and activation of PI3K. GI hormones increasing intracellular cAMP had similar effects. However, GI-hormones/neurotransmitters [CCK, bombesin, carbachol] activating phospholipase C (PLC) inhibited basal and growth-factor-stimulated Akt activation. Detailed studies with CCK, which has both physiological and pathophysiological effects on pancreatic acinar cells at different concentrations, demonstrated CCK has a biphasic effect: at low concentrations (pM) stimulating Akt by a Src-dependent mechanism and at higher concentrations (nM) inhibited basal and stimulated Akt translocation, phosphorylation and activation, by de-phosphorylating p85 resulting in decreasing PI3K activity. This effect required activation of both limbs of the PLC-pathway and a protein tyrosine phosphatase, but was not mediated by p44/42 MAPK, Src or activation of a serine phosphatase. Akt inhibition by CCK was also found in vivo and in Panc-1 cancer cells where it inhibited serum-mediated rescue from apoptosis. These results demonstrate that GI growth factors as well as gastrointestinal hormones/neurotransmitters with different cellular basis of action can all regulate Akt phosphorylation in pancreatic acinar cells. This regulation is complex with phospholipase C agents such as CCK, because both stimulatory and inhibitory effects can be seen, which are mediated by different mechanisms.

The novel protein kinase C isoforms -delta and -epsilon modulate caerulein-induced zymogen activation in pancreatic acinar cells

Isoforms of protein kinase C (PKC) have been shown to modulate some cellular responses such as pathological secretion and generation of inflammatory mediators during acute pancreatitis (AP). We propose that PKC also participates in premature zymogen activation within the pancreatic acinar cell, a key event in the initiation of AP. This hypothesis was examined in in vivo and cellular models of caerulein-induced AP using PKC activators and inhibitors. Phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA, 200 nM), a known activator of PKC, enhanced zymogen activation at both 0.1 nM and 100 nM caerulein, concentrations which mimic physiological and supraphysiological effects of the hormone cholecystokinin, respectively, in preparations of pancreatic acinar cells. Isoform-specific PKC inhibitors for PKC-delta and PKC-epsilon reduced supraphysiological caerulein-induced zymogen activation. Using a cell-free reconstitution system, we showed that inhibition of PKC-delta and -epsilon, reduced zymogen activation in both zymogen granule-enriched and microsomal fractions. In dispersed acinar cells, 100 nM caerulein stimulation caused PKC-delta and -epsilon isoform translocation to microsomal membranes using cell fractionation and immunoblot analysis. PKC translocation was confirmed with in vivo studies and immunofluorescence microscopy in pancreatic tissues from rats treated with or without 100 nM caerulein. PKC-epsilon redistributed from an apical to a supranuclear region following caerulein administration. The signal for PKC-epsilon overlapped with granule membrane protein, GRAMP-92, an endosomal/lysosomal marker, in a supranuclear region where zymogen activation takes place. These results indicate that PKC-delta and -epsilon isoforms translocate to specific acinar cell compartments and modulate zymogen activation.

CCK causes PKD1 activation in pancreatic acini by signaling through PKC-delta and PKC-independent pathways

Protein kinase D1 (PKD1) is involved in cellular processes including protein secretion, proliferation and apoptosis. Studies suggest PKD1 is activated by various stimulants including gastrointestinal (GI) hormones/neurotransmitters and growth factors in a protein kinase C (PKC)-dependent pathway. However, little is known about the mechanisms of PKD1 activation in physiologic GI tissues. We explored PKD1 activation by GI hormones/neurotransmitters and growth factors and the mediators involved in rat pancreatic acini. Only hormones/neurotransmitters activating phospholipase C caused PKD1 phosphorylation (S916, S744/748). CCK activated PKD1 and caused a time- and dose-dependent increase in serine phosphorylation by activation of high- and low-affinity CCK(A) receptor states. Inhibition of CCK-stimulated increases in phospholipase C, PKC activity or intracellular calcium decreased PKD1 S916 phosphorylation by 56%, 62% and 96%, respectively. PKC inhibitors GF109203X/Go6976/Go6983/PKC-zeta pseudosubstrate caused a 62/43/49/0% inhibition of PKD1 S916 phosphorylation and an 87/13/82/0% inhibition of PKD1 S744/748 phosphorylation. Expression of dominant negative PKC-delta, but not PKC-epsilon, or treatment with PKC-delta translocation inhibitor caused marked inhibition of PKD phosphorylation. Inhibition of Src/PI3K/MAPK/tyrosine phosphorylation had no effect. In unstimulated cells, PKD1 was mostly located in the cytoplasm. CCK stimulated translocation of total and phosphorylated PKD1 to the membrane. These results demonstrate that CCK(A) receptor activation leads to PKD activation by signaling through PKC-dependent and PKC-independent pathways.

Ethanol sensitizes NF-kappaB activation in pancreatic acinar cells through effects on protein kinase C-epsilon

Although ethanol abuse is the most common cause of pancreatitis, the mechanism of alcohol's effect on the pancreas is not well understood. Previously, we demonstrated that in vitro ethanol treatment of pancreatic acinar cells augmented the CCK-8-induced activation of NF-kappaB, a key signaling system involved in the inflammatory response of pancreatitis. In the present study, we determine the role for individual PKC isoforms in the sensitizing effect of ethanol on NF-kappaB activation. Dispersed rat pancreatic acini were treated with and without ethanol and then stimulated with CCK-8; 100 nM CCK-8 caused both NF-kappaB and PKC-delta, -epsilon, and -zeta activation, whereas 0.1 nM CCK-8 did not increase PKC-epsilon, PKC-zeta, or NF-kappaB activity. CCK-8 (0.1 nM) did activate PKC-delta. PKC-epsilon activator alone did not cause NF-kappaB activation; however, together with 0.1 nM CCK-8, it caused NF-kappaB activation. Ethanol activated PKC-epsilon without affecting other PKC isoforms or NF-kappaB activity. Of note, stimulation of acini with ethanol and 0.1 nM CCK-8 resulted in the activation of PKC-delta, PKC-epsilon, and NF-kappaB. The NF-kappaB activation to 0.1 nM CCK-8 in ethanol-pretreated acini was inhibited by both PKC-delta inhibitor and PKC-epsilon inhibitor. Taken together, these results demonstrate the different modes of activation of PKC isoforms and NF-kappaB in acini stimulated with ethanol, high-dose CCK-8, and low-dose CCK-8, and furthermore suggest that activation of both PKC-epsilon and -delta is required for NF-kappaB activation. These results suggest that ethanol enhances the CCK-8-induced NF-kappaB activation at least in part through its effects on PKC-epsilon.

Protein kinase C modulates the pulmonary inflammatory response in acute pancreatitis

The present study aims at evaluating the role of protein kinase C (PKC) in the development of acute lung injury, production of inflammatory mediators and expression of adhesion molecules on leukocytes after induction of acute pancreatitis (AP). AP was induced by the intraductal infusion of 5% sodium taurodeoxycholate in the rat. The animals had the PKC inhibitor polymyxin B administered intraperitoneally 30min prior to induction of AP. Levels of protein content, protease activity, cytokines and chemokines in bronchoalveolar lavage fluid (BALF) were assessed 1 and 6h after AP induction. Adhesion molecule expression on leukocytes were measured by flowcytometry. Pretreatment with polymyxin B prevented against acute pancreatitis-induced lung injury and the otherwise occurring increases in TNF-alpha, IL-1beta, MCP-1 and IL-10, as well as against the decreases in IL-2, IFNgamma and TIMP-1, decreased protease activity and down-regulation of CD31, CD54 and CD62L on recruited neutrophils and macrophages in BALF. The results indicate that the leukocyte response in acute pancreatitis vary depending on leukocyte subpopulation. It seems that activation of the PKC signalling pathway may play an important role in pancreatitis-associated lung injury.

Rottlerin inhibits stimulated enzymatic secretion and several intracellular signaling transduction pathways in pancreatic acinar cells by a non-PKC-delta-dependent mechanism

Protein kinase C-delta (PKC-delta) becomes activated in pancreatic acini in response to cholecystokinin (CCK) and plays a pivotal role in the exocrine pancreatic secretion. Rottlerin, a polyphenolic compound, has been widely used as a potent and specific PKC-delta inhibitor. However, some recent studies showed that rottlerin was not effective in inhibiting PKCdelta activity in vitro and that may display unspecific effects. The aims of this work were to investigate the specificity of rottlerin as an inhibitor of PKC-delta activity in intact cells and to elucidate the biochemical causes of its unspecificity. Preincubation of pancreatic acini with rottlerin (6 microM) inhibited CCK-stimulated translocation, tyrosine phosphorylation (TyrP) and activation of PKC-delta in pancreatic acini in a time-dependent manner. Rottlerin inhibited amylase secretion stimulated by both PKC-dependent pathways (CCK, bombesin, carbachol, TPA) and also by PKC-independent pathways (secretin, VIP, cAMP analogue). CCK-stimulation of MAPK activation and p125(FAK) TyrP which are mediated by PKC-dependent and -independent pathways were also inhibited by rottlerin. Moreover, rottlerin rapidly depleted ATP content in pancreatic acini in a similar way as the mitochondrial uncouplers CCCP and FCCP. All studied inhibitory effects of rottlerin in pancreatic acini were mimicked by FCCP (agonists-stimulated amylase secretion, p125(FAK) TyrP, MAPK activation and PKC-delta TyrP and translocation). Finally, rottlerin as well as FCCP display a potent inhibitory effect on the activation of other PKC isoforms present in pancreatic acini. Our results suggest that rottlerin effects in pancreatic acini are not due to a specific PKC-delta blockade, but likely due to its negative effect on acini energy resulting in ATP depletion. Therefore, to study the role of PKC-delta in cellular processes using rottlerin it is essential to keep in mind that may deplete ATP levels and inhibit different PKC isoforms. Our results give reasons for a more careful choice of rottlerin for PKC-delta investigation.

Regulation of CCK-induced amylase release by PKC-delta in rat pancreatic acinar cells

PKC is known to be activated by pancreatic secretagogues such as CCK and carbachol and to participate along with calcium in amylase release. Four PKC isoforms, alpha, delta, epsilon, and zeta, have been identified in acinar cells, but which isoforms participate in amylase release are unknown. To identify the responsible isoforms, we used translocation assays, chemical inhibitors, and overexpression of individual isoforms and their dominant-negative variants by means of adenoviral vectors. CCK stimulation caused translocation of PKC-alpha, -delta, and -epsilon, but not -zeta from soluble to membrane fraction. CCK-induced amylase release was inhibited approximately 30% by GF109203X, a broad spectrum PKC inhibitor, and by rottlerin, a PKC-delta inhibitor, but not by Gö6976, a PKC-alpha inhibitor, at concentrations from 1 to 5 microM. Neither overexpression of wild-type or dominant-negative PKC-alpha affected CCK-induced amylase release. Overexpression of PKC-delta and -epsilon enhanced amylase release, whereas only dominant-negative PKC-delta inhibited amylase release by 25%. PKC-delta overexpression increased amylase release at all concentrations of CCK, but dominant-negative PKC-delta only inhibited the maximal concentration; both similarly affected carbachol and JMV-180-induced amylase release. Overexpression of both PKC-delta and its dominant-negative variant affected the late but not the early phase of amylase release. GF109203X totally blocked the enhancement of amylase release by PKC-delta but had no further effect in the presence of dominant-negative PKC-delta. These results indicate that PKC-delta is the PKC isoform involved with amylase secretion.

PKC-delta and -epsilon regulate NF-kappaB activation induced by cholecystokinin and TNF-alpha in pancreatic acinar cells

Although NF-kappaB plays an important role in pancreatitis, mechanisms underlying its activation remain unclear. We investigated the signaling pathways mediating NF-kappaB activation in pancreatic acinar cells induced by high-dose cholecystokinin-8 (CCK-8), which causes pancreatitis in rodent models, and TNF-alpha, which contributes to inflammatory responses of pancreatitis, especially the role of PKC isoforms. We determined subcellular distribution and kinase activities of PKC isoforms and NF-kappaB activation in dispersed rat pancreatic acini. We applied isoform-specific, cell-permeable peptide inhibitors to assess the role of individual PKC isoforms in NF-kappaB activation. Both CCK-8 and TNF-alpha activated the novel isoforms PKC-delta and -epsilon and the atypical isoform PKC-zeta but not the conventional isoform PKC-alpha. Inhibition of the novel PKC isoforms but not the conventional or the atypical isoform resulted in the prevention of NF-kappaB activation induced by CCK-8 and TNF-alpha. NF-kappaB activation by CCK-8 and TNF-alpha required translocation but not tyrosine phosphorylation of PKC-delta. Activation of PKC-delta, PKC-epsilon, and NF-kappaB with CCK-8 involved both phosphatidylinositol-specific PLC and phosphatidylcholine (PC)-specific PLC, whereas with TNF-alpha they only required PC-specific PLC for activation. Results indicate that CCK-8 and TNF-alpha initiate NF-kappaB activation by different PLC pathways that converge at the novel PKCs (delta and epsilon) to mediate NF-kappaB activation in pancreatic acinar cells. These findings suggest a key role for the novel PKCs in pancreatitis.

Ethanol modifies the actin cytoskeleton in rat pancreatic acinar cells--comparison with effects of CCK

BACKGROUND

One of the early events leading to alcoholic pancreatitis seems to be the effect of ethanol on stimulus-secretion coupling. This study examines ethanol-induced modifications of filamentous actin (F-actin) content and localization in acini, the resulting alpha-amylase secretion and the role of protein kinase C (PKC) activity in these processes.

METHODS

Freshly isolated acini were treated with different concentrations of ethanol or cholecystokinin octapeptide (CCK-8) for different periods. F-actin was localized by confocal laser scanning microscopy; its quantity was determined fluorometrically, and the alpha-amylase secretion was measured.

RESULTS

Ethanol caused F-actin reorganization resembling the effects of supramaximal CCK-8 stimulation and of direct PKC activation by phorbol-12-myristate-13-acetate. The polyphasic time course of the F-actin content also resembled that under supramaximal CCK-8 stimulation and was counteracted by inhibition of PKC. The PKC inhibitor bisindolylmaleimide I did not increase the ethanol- induced alpha-amylase secretion, but the suboptimally CCK-8-stimulated secretion via high-affinity receptors.

CONCLUSION

Ethanol, like supramaximal CCK-8 concentrations, inhibits acinar secretion by reorganization of the actin cytoskeleton via PKC activation. This effect is suggested to be mediated by low-affinity CCK-A receptors. Together with the ethanol-induced stimulation of early steps of stimulus-secretion coupling, this may be a pancreas-damaging mechanism resembling that in experimental hyperstimulation pancreatitis.

Ethanol differentially regulates NF-kappaB activation in pancreatic acinar cells through calcium and protein kinase C pathways

Mechanisms of alcoholic pancreatitis remain unknown. Previously, we showed that ethanol feeding sensitizes rats to pancreatitis caused by CCK-8, at least in part, by augmenting activation of the proinflammatory transcription factor NF-kappaB. To elucidate the mechanism of sensitization, here we investigate the effect of ethanol on Ca(2+)- and PKC-mediated pathways of CCK-induced NF-kappaB activation using an in vitro system of rat pancreatic acini incubated with ethanol. Ethanol augmented CCK-8-induced activation of NF-kappaB, similar to our in vivo findings with ethanol-fed rats. In contrast, ethanol prevented NF-kappaB activation caused by thapsigargin, an agent that mobilizes intracellular Ca(2+) bypassing the receptor. Pharmacological analysis showed that NF-kappaB activation by thapsigargin but not by CCK-8 is mediated through the calcineurin pathway and that the inhibitory effect of ethanol on the thapsigargin-induced NF-kappaB activation could be through inhibiting this pathway. Ethanol augmented NF-kappaB activation induced by the phorbol ester PMA, a direct activator of PKC. Inhibitory analysis demonstrated that Ca(2+)-independent (novel and/or atypical) PKC isoforms are involved in NF-kappaB activation induced by both CCK-8 and PMA in cells treated and not treated with ethanol. The results indicate that ethanol differentially affects the Ca(2+)/calcineurin- and PKC-mediated pathways of NF-kappaB activation in pancreatic acinar cells. These effects may play a role in the ability of ethanol to sensitize pancreas to the inflammatory response and pancreatitis.

Cholecystokinin-stimulated protein kinase C-delta kinase activation, tyrosine phosphorylation, and translocation are mediated by Src tyrosine kinases in pancreatic acinar cells

Protein kinase C-delta (PKC-delta) is involved in growth, differentiation, tumor suppression, and regulation of other cellular processes. PKC-delta activation causes translocation, tyrosine phosphorylation, and serine-threonine kinase activity. However, little is known about the ability of G protein-coupled receptors to activate these processes or the mediators involved. In the present study, we explored the ability of the neurotransmitter/hormone, CCK, to stimulate these changes in PKC-delta and explored the mechanisms. In rat pancreatic acini under basal conditions, PKC-delta is almost exclusively located in cytosol. CCK and TPA stimulated a rapid PKC-delta translocation to membrane and nuclear fractions, which was transient with CCK. CCK stimulated rapid tyrosine phosphorylation of PKC-delta and increased kinase activity. Using tyrosine kinase (B44) and a tyrosine phosphatase inhibitor (orthovanadate), changes in both CCK- and TPA-stimulated PKC-delta tyrosine phosphorylation were shown to correlate with changes in its kinase activity but not translocation. Both PKC-delta tyrosine phosphorylation and activation occur exclusively in particulate fractions. The Src kinase inhibitors, SU6656 and PP2, but not the inactive related compound, PP3, inhibited CCK- and TPA-stimulated PKC-delta tyrosine phosphorylation and activation. In contrast, PP2 also had a lesser effect on CCK- but not TPA-stimulated PKC-delta translocation. CCK stimulated the association of Src kinases with PKC-delta, demonstrated by co-immunoprecipitation. These results demonstrate that CCKA receptor activation results in rapid translocation, tyrosine phosphorylation, and activation of PKC-delta. Stimulation of PKC-delta translocation precedes tyrosine phosphorylation, which is essential for activation to occur. Activation of Src kinases is essential for the tyrosine phosphorylation and kinase activation to occur and plays a partial role in translocation.

Caerulein-induced pancreatitis and islet blood flow in anesthetized rats

BACKGROUND

Microcirculatory mechanisms have been suggested to be involved in the development of acute pancreatitis. Islet blood flow has not previously been studied in this disease. The present study aimed to investigate the effects of caerulein-induced pancreatitis on pancreatic blood perfusion, especially islet blood flow.

MATERIALS AND METHODS

Continuous 4 h caerulein-infusion was used to induce mild, edemateous pancreatitis in anesthetized Sprague-Dawley rats. Some animals were then given an additional 2 h infusion of saline. Thus, at 4 or 6 h after initiating caerulein infusion the blood flow to the pancreas, pancreatic islets, and intestines was measured with a microsphere technique.

RESULTS

All infused animals demonstrated an edemateous pancreatitis, without hemorrhages. Both total pancreatic and islet blood flow was increased after the 4-h infusion. However, the increase was less pronounced in the islets. After an additional 2 h with only saline infused, the blood flow values in rats initially infused with caerulein were lower than at 4 h, but total pancreatic blood was still higher than in control rats. No effects on intestinal blood flow values were seen.

CONCLUSIONS

Pancreatic islet blood flow in rats with mild edematous pancreatitis is increased, but not to the same extent as that in the whole pancreas.

Phosphospecific site tyrosine phosphorylation of p125FAK and proline-rich kinase 2 is differentially regulated by cholecystokinin receptor type A activation in pancreatic acini

The focal adhesion kinases, p125FAK and proline-rich kinase 2 (PYK2), are involved in numerous processes as adhesion, cytoskeletal changes, and growth. These kinases have 45% homology and share three tyrosine phosphorylation (TyrP) sites. Little information exists on the ability of stimulants to cause TyrP of each kinase site and the cellular mechanism involved. We explored the ability of the neurotransmitter/hormone, CCK, to stimulate TyrP at each site. In rat pancreatic acini, CCK stimulated TyrP at each site in both kinases. TyrP was rapid except for pY397FAK. The magnitude of TyrP differed with the different FAK and PYK2 sites. The CCK dose-response curve for TyrP for sites in each kinase was similar. CCK-JMV, an agonist of the high affinity receptor state and antagonist of the low affinity receptor state, was less efficacious than CCK at each FAK/PYK2 site and inhibited CCK maximal stimulation. Thapsigargin decreased CCK-stimulated TyrP of pY402PYK2 and pY925FAK but not the other sites. GF109203X reduced TyrP of only the PYK2 sites, pY402 and pY580. GF109203X with thapsigargin decreased TyrP of pY402PYK2 and the three FAK sites more than either inhibitor alone. Basal TyrP of pY397FAK was greater than other sites. These results demonstrate that CCK stimulates tyrosine phosphorylation of each of the three homologous phosphorylation sites in FAK and PYK2. However, CCK-stimulated TyrP at these sites differs in kinetics, magnitude, and participation of the high/low affinity receptor states and by protein kinase C and [Ca2+]i. These results show that phosphorylation of these different sites is differentially regulated and involves different intracellular mechanisms in the same cell.

Cholecystokinin stimulates extracellular signal-regulated kinase through activation of the epidermal growth factor receptor, Yes, and protein kinase C. Signal amplification at the level of Raf by activation of protein kinase Cepsilon

Cholecystokinin (CCK) and related peptides are potent growth factors in the gastrointestinal tract and may be important for human cancer. CCK exerts its growth modulatory effects through G(q)-coupled receptors (CCK(A) and CCK(B)) and activation of extracellular signal-regulated protein kinase 1/2 (ERK1/2). In the present study, we investigated the different mechanisms participating in CCK-induced activation of ERK1/2 in pancreatic AR42J cells expressing both CCK(A) and CCK(B). CCK activated ERK1/2 and Raf-1 to a similar extent as epidermal growth factor (EGF). Inhibition of EGF receptor (EGFR) tyrosine kinase or expression of dominant-negative Ras reduced CCK-induced ERK1/2 activation, indicating participation of the EGFR and Ras in CCK-induced ERK1/2 activation. However, compared with EGF, CCK caused only small increases in tyrosine phosphorylation of the EGFR and Shc, Shc-Grb2 complex formation, and Ras activation. Signal amplification between Ras and Raf in a CCK-induced ERK cascade appears to be mediated by activation of protein kinase Cepsilon (PKCepsilon), because 1) down-modulation of phorbol ester-sensitive PKCs inhibited CCK-induced activation of Ras, Raf, and ERK1/2 without influencing Shc-Grb2 complex formation; 2) PKCepsilon, but not PKCalpha or PKCdelta, was detectable in Raf-1 immunoprecipitates, although CCK activated all three PKC isoenzymes. In addition, the present study provides evidence that the Src family tyrosine kinase Yes is activated by CCK and mediates CCK-induced tyrosine phosphorylation of Shc. Furthermore, we show that CCK-induced activation of the EGFR and Yes is achieved through the CCK(B) receptor. Together, our data show that different signals emanating from the CCK receptors mediate ERK1/2 activation; activation of Yes and the EGFR mediate Shc-Grb2 recruitment, and activation of PKC, most likely PKCepsilon, augments CCK-stimulated ERK1/2 activation at the Ras/Raf level.

Alterations in PKCgamma in the mouse hippocampus after prenatal exposure to heroin: a link from cell signaling to behavioral outcome

Administration of heroin to pregnant mice evokes neurochemical and behavioral deficits consequent to disruption of septohippocampal cholinergic innervation, notably involving desensitization of the ability of cholinergic receptors to activate PKC activity. The present study further evaluates whether desensitization occurs specifically for the PKCgamma isoform, the behaviorally relevant subtype, as compared to PKCalpha. Mice were exposed transplacentally to heroin on gestational days (GD) 9-18 via s.c. maternal injections (10 mg/kg per day). In young adulthood (50 days old), control offspring showed an increase in hippocampal cell membrane PKCgamma after incubation with the muscarinic cholinergic receptor agonist, carbachol, indicative of translocation from the cytosol. Prenatal exposure to heroin eliminated this response, whereas basal PKCgamma levels were unchanged. In contrast, PKCalpha, which is not related to heroin-induced behavioral deficits, did not show a loss of response. The present findings strongly point to abnormalities in the responsiveness of PKCgamma as a mechanism underlying the neurobehavioral teratogenicity of heroin.

Cholecystokinin-stimulated tyrosine phosphorylation of PKC-delta in pancreatic acinar cells is regulated bidirectionally by PKC activation

PKC-delta is important in cell growth, apoptosis, and secretion. Recent studies show its stability is regulated by tyrosine phosphorylation (TYR-P), which can be stimulated by a number of agents. Many of these stimuli also activate phospholipase C (PLC) cascades and little is known about the relationship between these cascades and PKC-delta TYR-P. Cholecystokinin (CCK) stimulates PKCs but it is unknown if it causes PKC-delta TYR-P and if so, the relationship between these cascades is unknown. In rat pancreatic acini, CCK-8 stimulated rapid PKC-delta TYR-P by activation of the low affinity CCK(A) receptor state. TPA had a similar effect. BAPTA did not decrease CCK-stimulated PKC-delta TYR-P but instead, increased it. A23187 did not stimulate PKC-delta TYR-P. Wortmannin and LY 294002 did not alter CCK-stimulated PKC-delta TYR-P. GF 109203X, at low concentrations, increased PKC-delta TYR-P stimulated by CCK or TPA and at higher concentrations, inhibited it. The cPKC inhibitors, Gö 6976 and safingol, caused a similar increase in TPA- and CCK-stimulated PKC-delta TYR-P. These results demonstrate that CCK(A) receptor activation causes PKC-delta TYR-P through activation of only one of its two receptor affinity states. This PKC-delta TYR-P is not directly influenced by changes in [Ca(2+)](i); however, the resultant activation of PKC-alpha has an inhibitory effect. Therefore, CCK activates both stimulatory and inhibitory PKC cascades regulating PKC-delta TYR-P and, hence, likely plays an important role in regulating PKC-delta degradation and cellular abundance.

Low-affinity CCK-1 receptors inhibit bombesin-stimulated secretion in rat pancreatic acini--implication of the actin cytoskeleton

EXPERIMENTAL OBJECTIVES

Stimulation of low-affinity CCK-1 receptors on pancreatic acini leads to inhibition of enzyme secretion. We studied signal transduction mechanisms to identify potential causes for the reduced secretion.

RESULTS

Co-stimulation experiments with CCK, CCK-JMV-180, and bombesin revealed an inhibition of bombesin-stimulated enzyme secretion by low-affinity CCK-1 receptors. Binding of 125I-gastrin-releasing peptide (the mammalian analogue of bombesin) to acini after CCK preincubation was not altered. After a short preincubation of acini with high concentrations of CCK, intracellular calcium remained responsive to bombesin. In contrast to bombesin or CCK at concentrations of 10(-10) M or lower, high concentrations of CCK caused a strong activation of p125 focal adhesion kinase (p125(FAK)) and a marked reorganisation of the actin cytoskeleton.

CONCLUSIONS

Inhibitory mechanisms triggered by low-affinity CCK-1 receptors interrupt enzyme secretion from pancreatic acini at late stages in the signal transduction cascades since bombesin receptor binding and early signalling events remained intact after CCK preincubation. A reorganisation of the actin cytoskeleton is suggested to be the mechanism by which low-affinity CCK-1 receptors actively interrupt enzyme secretion stimulated by other receptors.

Intracellular signaling mechanisms activated by cholecystokinin-regulating synthesis and secretion of digestive enzymes in pancreatic acinar cells

The intracellular signaling mechanisms by which cholecystokinin (CCK) and other secretagogues regulate pancreatic acinar function are more complex than originally realized. CCK couples through heterotrimeric G proteins of the Gq family to lead to an increase in intracellular free Ca2+, which shows spatial and temporal patterns of signaling. The actions of Ca2+ are mediated in part by activation of a number of Ca2+-activated protein kinases and the protein phosphatase calcineurin. By the process of exocytosis the intracellular messengers Ca2+, diacylglycerol, and cAMP activate the release of the zymogen granule content in a manner that is poorly understood. This fusion event most likely involves SNARE and Rab proteins present on zymogen granules and cellular membrane domains. More likely related to nonsecretory aspects of cell function, CCK also activates three MAPK cascades leading to activation of ERKs, JNKs, and p38 MAPK. Although the function of these pathways is not well understood, ERKs are probably related to cell growth, and through phosphorylation of hsp27, p38 can affect the actin cytoskeleton. The PI3K (phosphatidylinositol 3-kinase)-mTOR (mammalian target of rapamycin) pathway is important for regulation of acinar cell protein synthesis because it leads to both activation of p70S6K and regulation of the availability of eIF4E in response to CCK. CCK also activates a number of tyrosyl phosphorylation events including that of p125FAK and other proteins associated with focal adhesions.

Carbachol stimulates TYR phosphorylation and association of PKCdelta and PYK2 in pancreas

Carbachol treatment resulted in increased phosphorylation on tyrosine of PKCdelta immunoprecipitated from rat pancreatic acinar cells. The Ca2+-dependent tyrosine kinase PYK2 coimmunoprecipitated with PKCdelta from carbachol-exposed cells and also exhibited increased tyrosine phosphorylation. Tyrosine phosphorylation of both PKCdelta and PYK2 was concentration-dependent with respect to carbachol, and rapid, reaching maximal levels by 5 min of treatment. Exposure of acinar cells to phorbol myristate acetate (PMA), a phorbol ester activator of PKCdelta, also resulted in increased phosphorylation of PKCdelta and PYK2 isolated using anti-PKCdelta immunoprecipitation. These results are suggestive of a physical and functional interaction between PKCdelta and PYK2 following muscarinic stimulation in the pancreatic acinar cell.

Caerulein-induced NF-kappaB/Rel activation requires both Ca2+ and protein kinase C as messengers

The eukaryotic transcription factor NF-kappaB/Rel is activated by a large variety of stimuli. We have recently shown that NF-kappaB/Rel is induced during the course of caerulein pancreatitis. Here, we show that activation of NF-kappaB/Rel by caerulein, a CCK analog, requires increasing intracellular Ca2+ levels and protein kinase C activation. Caerulein induces a dose-dependent increase of nuclear NF-kappaB/Rel binding activity in pancreatic lobules, which is paralleled by degradation of IkappaBalpha. IkappaBbeta was only slightly affected by caerulein treatment. Consistent with an involvement of Ca2+, the endoplasmic reticulum-resident Ca2+-ATPase inhibitor thapsigargin activated NF-kappaB/Rel in pancreatic lobules. The intracellular Ca2+ chelator TMB-8 prevented IkappaBalpha degradation and subsequent nuclear translocation of NF-kappaB/Rel induced by caerulein. BAPTA-AM was less effective. Cyclosporin A, a Ca2+/calmodulin-dependent protein phosphatase (PP2B) inhibitor, decreased caerulein-induced NF-kappaB/Rel activation and IkappaBalpha degradation. The inhibitory effect of bisindolylmaleimide suggests that protein kinase C activity is also required for caerulein-induced NF-kappaB/Rel activation. These data suggest that Ca2+- as well as protein kinase C-dependent mechanisms are required for caerulein-induced NF-kappaB/Rel activation.

Secretagogues cause ubiquitination and down-regulation of inositol 1, 4,5-trisphosphate receptors in rat pancreatic acinar cells

BACKGROUND & AIMS

The action of several exocrine pancreas secretagogues depends on the second messenger inositol 1,4, 5-trisphosphate (IP3), which, via endoplasmic reticulum-located IP3 receptors, mobilizes intracellular Ca2+ stores. Signaling pathways like this one are regulated at multiple loci. To determine whether IP3 receptors are one of these loci, we measured IP3 receptor concentration, distribution, and modification in secretagogue-stimulated rat pancreatic acinar cells.

METHODS

Isolated rat pancreatic acinar cells were exposed to cholecystokinin and other secretagogues, or rats were injected intraperitoneally with cerulein. Then samples of cells or pancreata were probed for IP3 receptor content and distribution as well as for ubiquitin association with IP3 receptors.

RESULTS

Secretagogues rapidly down-regulated acinar cell IP3 receptors both in vitro and in vivo. They also elicited receptor redistribution and caused receptors to become ubiquitinated, indicating that the ubiquitin/proteasome proteolytic pathway contributes to the down-regulation. Surprisingly, however, proteasome inhibitors did not block IP3 receptor down-regulation, and phospholipase Cbeta1 and protein kinase C also were down-regulated. Thus, secretagogues simultaneously activate an additional proteolytic pathway.

CONCLUSIONS

Secretagogues rapidly down-regulate IP3 receptors and other proteins involved in intracellular signaling by a mechanism that involves, but is not limited to, the ubiquitin/proteasome pathway. Loss of these proteins may account for the disruption of Ca2+ mobilization that occurs in models of acute pancreatitis, and may contribute to cell adaptation under physiological conditions.

Redistribution of protein kinase C isoforms in rat pancreatic acini during lactation and weaning

Freshly enzymatically isolated pancreatic acini from lactating and weaning Wistar rats were used to investigate the role of protein kinase C (PKC) isoforms during these physiologically relevant pancreatic secretory and growth processes. The combination of immunoblot and immunohistochemical analysis shows that the PKC isoforms alpha, delta, and epsilon are present in pancreatic acini from control, lactating and weaning rats. A vesicular distribution of PKC-alpha, -delta, and -epsilon was detected by immunohistochemical analysis in the pancreatic acini from all the experimental groups. PKC-delta showed the strongest PKC immunoreactivity (PKC-IR). In this vesicular distribution, PKC-IR was located at the apical region of the acinar cells. No differences were observed between control, lactating and weaning rats. However, the immunoblot analysis of pancreatic PKC isoforms during lactation and weaning showed a significant translocation of PKC-delta from the cytosol to the membrane fraction when compared with control animals. Translocation of PKC isoforms (alpha, delta and epsilon) in response to 12-O-tetradecanoyl phorbol 13-acetate (TPA) 1 microM (15 min, 37 degrees C) was comparable in pancreatic acini from control, lactating and weaning rats. In the control group, a significant translocation of all the isoforms (alpha, delta and epsilon) from the cytosol to the membrane was observed. The PKC isoform most translocated by TPA was PKC-delta. In contrast, no statistically significant increase in PKC-delta translocation was detected in pancreatic acini isolated from lactating or weaning rats. These results suggest that the PKC isoforms are already translocated to the surface of the acinar cells from lactating or weaning rats. In addition, they suggest that isoform specific spatial PKC distribution and translocation occur in association with the growth response previously described in the rat exocrine pancreas during lactation and weaning.

Ca2+ and protein kinase C activation of mucin granule exocytosis in permeabilized SPOC1 cells

Mucin secretion by airway goblet cells is under the control of apical P2Y2, phospholipase C-coupled purinergic receptors. In SPOC1 cells, the mobilization of intracellular Ca2+ by ionomycin or the activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) stimulates mucin secretion in a fully additive fashion [L. H. Abdullah, J. D. Conway, J. A. Cohn, and C. W. Davis. Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17): L201-L210, 1997]. This apparent independence between PKC and Ca2+ in the stimulation of mucin secretion was tested in streptolysin O-permeabilized SPOC1 cells. These cells were fully competent to secrete mucin when Ca2+ was elevated from 100 nM to 3.1 microM for 2 min following permeabilization; the Ca2+ EC50 was 2.29 +/- 0.07 microM. Permeabilized SPOC1 cells were exposed to PMA or 4alpha-phorbol at Ca2+ activities ranging from 10 nM to 10 microM. PMA, but not 4alpha-phorbol, increased mucin release at all Ca2+ activities tested: at 10 nM Ca2+ mucin release was 2.1-fold greater than control and at 4.7 microM Ca2+ mucin release was maximal (3.6-fold increase). PMA stimulated 27% more mucin release at 4.7 microM than at 10 nM Ca2+. Hence, SPOC1 cells possess Ca2+-insensitive, PKC-dependent, and Ca2+-dependent PKC-potentiated pathways for mucin granule exocytosis.

Distinct phospholipase C-regulated signalling pathways in Swiss 3T3 fibroblasts induce the rapid generation of the same polyunsaturated diacylglycerols

Prostaglandin F2alpha, platelet-derived growth factor (PDGF) and calcium ionophore A23187 stimulated the rapid (within 25 s) generation of polyunsaturated 1,2-diacylglycerol (DAG) species, in particular 18:0/20:3n-9, 18:0/20:4n-6 and 18:0/20:5n-3, in Swiss 3T3 fibroblasts. This was followed by a second sustained phase characterised by saturated, monounsaturated and diunsaturated DAG species derived, at least partially, from a phospholipase D/phosphatidate phosphohydrolase-linked pathway. This could be directly activated by phorbol ester. Assay of rat brain protein kinase C (PKC) in lipid vesicles showed that first phase, polyunsaturated-enriched DAG isolated from Swiss 3T3 cells was a more potent activator of kinase activity compared to that achieved with DAG from control or 5 min stimulated cells. Thus activation of distinct members of the phospholipase C family leads to the rapid and almost identical generation of polyunsaturated DAG species which are capable of preferentially activating protein kinase C (PKC).

Protein kinase C isoform expression and function in transformed and non-transformed pancreatic acinar cell lines

Members of the protein kinase C (PKC) family of multifunctional serine/threonine phosphorylating enzymes are believed to play a role in regulating cellular differentiation and proliferation in many cell types. In the present study, we examined the expression of PKC isoforms in non-transformed (BMRPA.430) and transformed (TUC3) rat pancreatic acinar cell lines and compared this to PKC expression in freshly dispersed acini from rat pancreas. BMRPA.430 cells maintain characteristics of normal acini and are not tumorigenic, whereas TUC3 cells do not express tight junctions or polygonal morphology and are tumorigenic. As reported previously, PKC alpha, delta, epsilon, and zeta are expressed in freshly prepared acini. Likewise, these isoforms were detected in both the BMRPA.430 and TUC3 cell lines. In addition, PKC theta, a novel isoform, was detected in all three cell types at low levels. We used two PKC inhibitors to examine the role of PKC in acinar cell proliferation. CGP 41 251, a selective PKC inhibitor, and Go 6976, an agent which specifically inhibits calcium-dependent PKC isoforms, inhibited cell proliferation of both cell lines. Translocation of PKC alpha to the membrane was not observed in either cell line. Hence, our data indicate that ras-induced transformation does not alter PKC isoform expression in pancreatic acinar cells and that activation of PKC alpha is involved with acinar cell growth.

Cholecystokinin-stimulated tyrosine phosphorylation of p125FAK and paxillin is mediated by phospholipase C-dependent and -independent mechanisms and requires the integrity of the actin cytoskeleton and participation of p21rho

Recent studies show that the effects of some oncogenes, integrins, growth factors and neuropeptides are mediated by tyrosine phosphorylation of the cytosolic kinase p125 focal adhesion kinase (p125(FAK)) and the cytoskeletal protein paxillin. Recently we demonstrated that cholecystokinin (CCK) C-terminal octapeptide (CCK-8) causes tyrosine phosphorylation of p125(FAK) and paxillin in rat pancreatic acini. The present study was aimed at examining whether protein kinase C (PKC) activation, calcium mobilization, cytoskeletal organization and small G-protein p21(rho) activation play a role in mediating the stimulation of tyrosine phosphorylation by CCK-8 in acini. CCK-8-stimulated phosphorylation of p125(FAK) and paxillin reached a maximum within 2.5 min. The CCK-8 dose response for causing changes in the cytosolic calcium concentration ([Ca2+]i) was similar to that for p125(FAK) and paxillin phosphorylation, and both were to the left of that for receptor occupation and inositol phosphate production. PMA increased tyrosine phosphorylation of both proteins. The calcium ionophore A23187 caused only 25% of the maximal stimulation caused by CCK-8. GF109203X, a PKC inhibitor, completely inhibited phosphorylation with PMA but had no effect on the response to CCK-8. Depletion of [Ca2+]i by thapsigargin had no effect on CCK-8-stimulated phosphorylation. Pretreatment with both GF109203X and thapsigargin decreased CCK-8-stimulated phosphorylation of both proteins by 50%. Cytochalasin D, but not colchicine, completely inhibited CCK-8- and PMA-induced p125(FAK) and paxillin phosphorylation. Treatment with Clostridium botulinum C3 transferase, which inactivates p21(rho), caused significant inhibition of CCK-8-stimulated p125(FAK) and paxillin phosphorylation. These results demonstrate that, in pancreatic acini, CCK-8 causes rapid p125(FAK) and paxillin phosphorylation that is mediated by both phospholipase C-dependent and -independent mechanisms. For this tyrosine phosphorylation to occur, the integrity of the actin, but not the microtubule, cytoskeleton is essential as well as the activation of p21(rho).

Cholecystokinin and psychiatric disorders : role in aetiology and potential of receptor antagonists in therapy

Cholecystokinin (CCK) is one of the most abundant neuropeptides in the brain. It is found in the highest levels in cortical and limbic structures and also in the basal ganglia. Two subtypes of CCK receptors have been described in the brain and gastrointestinal tissues. CCK(A) (alimentary subtype) receptors are mainly located in the gastrointestinal tract, regulating secretion of enzymes from the pancreas and emptying of the gallbladder. However, CCK(A) receptors are also found in several brain regions, with the highest densities in structures poorly protected by the haematoencephalic barrier (the area postrema, nucleus tractus solitarius and hypothalamus). The distribution of CCK(B) (brain subtype) receptors overlaps with the localisation of CCK and its mRNA in different brain areas, with the highest densities in the cerebral cortex, basal ganglia, nucleus accumbens and forebrain limbic structures.Both subtype of CCK receptor belong to the guanine nucleotide-binding protein-(G protein)-linked receptor superfamily containing 7 transmembrane domains. Signal transduction at CCK receptors is mediated via G(q) protein-related activation of phospholipase C and the formation of inositol 1,4,5-triphosphate (IP(3)) and 1,2-diacylglycerol (DAG). Recent cloning of CCK(A) and CCK(B) receptors has shown that mRNA for both receptors is distributed in the same tissues as established in radioligand binding and receptor autoradiography studies, with few exceptions.The existence of multiple CCK receptors has fuelled the development of selective CCK(A) and CCK(B) receptor antagonists. These antagonists belong to distinct chemical groups, including dibutyryl derivatives of cyclic nucleotides, amino acid derivatives, partial sequences and derivatives of the -COOH terminal sequence heptapeptides of CCK, benzodiazepine derivatives, 'peptoids' based on fragments of the CCK molecule, and pyrazolidinones. At the present time, the compounds of choice for blockade of the CCK(A) receptor are lorglumide, devazepide and lintitript (SR27897). L-365,260, CI-988, L-740,093 and LY288513 are the drugs most widely used to block CCK(B) receptors.Studies with CCK antagonists (and agonists) in animals and humans suggest a role for CCK in the regulation of anxiety and panic. The administration of CCK agonists [ceruletide (caerulein), CCK-4, pentagastrin] has an anxiogenic action in various animal models and in different animal species. However, the anxiogenic action of CCK agonists is restricted to nonconditioned (ethological) models of anxiety, with very limited activity in the 'classical' conditioned models. Pharmacological studies have revealed that CCK(B) receptors are the key targets in the anxiogenic action of CCK agonists. Nevertheless, CCK(B) antagonists displayed very little activity, if any at all, in these models, but strongly antagonised the effects of CCK(B) agonists. The anxiogenic/panicogenic action of CCK(B) agonists (CCK-4, pentagastrin) is even more pronounced in human studies, but the effectiveness of CCK(B) antagonists as anxiolytics remains unclear. Clinical trials performed to date have provided inconclusive data about the anxiolytic potential of CCK(B) receptor antagonists, probably because of limiting pharmacokinetic factors.The results of some animal experiments suggest a role for CCK in depression. The administration of CCK(B) antagonists causes antidepressant-like action in mouse models of depression. However, human studies replicating this result have yet to be carried out.A prominent biochemical alteration in schizophrenia is a reduction of CCK levels in the cerebral cortex. This change may be related to the loss of cortical neurons, due to the schizophrenic process itself. In animal studies (mainly in mice), administration of CCK agonists and antagonists has been shown to be effective in several models, reflecting a possible antipsychotic activity of these drugs. However, the data obtained in human studies suggest that CCK agonists and antagonists do not improve the symptoms of schizophrenia. Taking into account the reduced levels of CCK and its receptors found in schizophrenia, treatments increasing, but not blocking, brain CCK activity may be more appropriate.

Phosphorylation of cholecystokinin receptors expressed on Chinese hamster ovary cells. Similarities and differences relative to native pancreatic acinar cell receptors

Phosphorylation of G protein-coupled receptors is an established mechanism for desensitization in response to agonist stimulation. We previously reported phosphorylation of the pancreatic acinar cell cholecystokinin (CCK) receptor and the establishment of two-dimensional phosphopeptide mapping of its sites of phosphorylation (Ozcelebi, F., and Miller, L. J. (1995) J. Biol. Chem. 270, 3435-3441). Here, we use similar techniques to map sites of phosphorylation of the same receptor expressed on a stable receptor-bearing Chinese hamster ovary (CHO)-CCKR cell line. Like the native cell, the CHO-CCKR cell receptor was phosphorylated in response to agonist stimulation in a concentration-dependent manner; however, the time course was quite different. CHO-CCKR cell receptor phosphorylation increased progressively to a plateau after 15 min, while in the acinar cell it peaks within 2 min and returns to baseline over this interval. There were distinct qualitative and quantitative differences in the sites of phosphorylation of the two receptor systems. One site previously attributed to action of a staurosporine-insensitive kinase in the acinar cell was absent in the CHO-CCKR cell. Site-directed mutagenesis was utilized to eliminate predicted sites of protein kinase C action, but only two of four such sites affected the phosphopeptide map of this receptor. Chemical and radiochemical sequencing were performed on these and other phosphopeptides which were present in both the CHO-CCKR cells and agonist-stimulated pancreatic acinar cells to provide direct evidence for the phosphorylation sites actually utilized. Thus, these data support the usefulness and limitations of a model cell system in studying receptor phosphorylation and desensitization.

High concentrations of cholecystokinin octapeptide suppress protein kinase C activity in guinea pig pancreatic acini

In pancreatic acini, calcium-mobilizing agents increase intracellular calcium and stimulate the production of diacylglycerol, and then activate protein kinase C (PKC). However, there are few studies which have examined the activation of PKC in intact acini. To examine the activation of PKC in intact acini by calcium-mobilizing agents, we measured the binding of [3H]phorbol-12,13-dibutyrate (PDBu) to intact acini. Acini were incubated with 10 nM [3H]PDBu at 25 degrees C with or without agents. The binding reactions were terminated by filtration. The filters were counted by a scintillation counter after washing. Acini possessed a single class of binding sites to PDBu, with Kd = 70 nM. CCK-8 and carbachol upregulated the binding affinity of PKC to PDBu in the acini. The ability of calcium-mobilizing agents to increase binding of [3H]PDBu to the acini had a close correlation to their ability to stimulate the amylase secretion from the acini, and higher concentrations of CCK-8 for amylase secretion suppressed binding of [3H]PDBu to the acini. 8Br-cAMP, 8Br-cGMP, and calcium ionophore did not inhibit the maximal activation of PKC induced by CCK-8. The calmodulin inhibitor W7 did not reverse the inhibitory effect of higher concentrations of CCK-8 on PKC activation. These results indicate that calcium-mobilizing agents upregulate the binding affinity of PKC to PDBu in intact acini, and that higher concentrations of CCK-8 for amylase secretion may activate the intracellular mechanism that inhibits PKC activity in acini. This inhibitory mechanism was mediated by some other mechanism other than cAMP-, cGMP-, calcium- and calmodulin-dependent mechanisms.

Cellular distribution of isoforms of protein kinase C (PKC) in pancreatic acini

As in a previous study (Biochim, Biophys. Acta 1224 (1994) 127-138), we used quantitative immunoblot analysis and found that rat pancreatic acini possess four different isoforms of PKC-alpha, delta, epsilon and zeta. The phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) caused translocation of each isoform from the cytosol to the membrane fraction. CCK-8 increased diacylglycerol (DAG) and caused translocation of PKC-sigma and PKC-epsilon but not that of PKC-alpha or PKC-zeta. L-364,718, a CCK receptor antagonist, prevented as well as reversed the effects of CCK-8 on DAG and on translocation of PKC-sigma and PKC-epsilon. To explore the possibility that different isoforms of PKC might have different distributions in rat pancreas, we used immunocytochemistry to determine the cellular distribution of different isoforms of PKC in intact pancreas as well as pancreatic acini. In intact pancreas, PKC-alpha and PKC-sigma were detected in islet cells but not in duct or acinar cells. PKC-epsilon was detected in the apical region of acinar cells and PKC-zeta was detected over the luminal surfaces of acinar cells and the ductules that extend from the acinus. Neither PKC-epsilon nor PKC-zeta was detected in islets. In pancreatic acini PKC-alpha and PKC-sigma were detected in islets or fragments of islets that contaminated the preparation but were not detected in acinar cells. PKC-epsilon was detected in the apical region of acinar cells and adding 1 microM TPA or 1 microM CCK-8 accentuated the immunostaining but did not alter its cellular distribution. L-364,718 reversed the changes in immunostaining caused by CCK-8. PKC-zeta was detected over the luminal surface of the acinar cells. TPA, but not CCK-8 or CCK-8 followed by L-364,718, increased the number of acini that showed staining of the luminal surfaces of acinar cells. Thus, the present results demonstrate that different isoforms of PKC are distributed differently in rat pancreas and that the different patterns of distribution can explain, at least in part, the different responses to CCK-8.

Characterization of the three different states of the cholecystokinin (CCK) receptor in pancreatic acini

By measuring binding of [125I]CCK-8 and [3H]L-364,718 to rat pancreatic acini we demonstrated directly that the pancreatic CCK receptor can exist in three different affinity states with respect to CCK--high affinity, low affinity and very low affinity. Binding of [125I]CCK-8 reflects interaction of the tracer with the high and low affinity states, whereas binding of [3H]L-364,718 reflects interaction of the tracer with the low and very low affinity states. Treating acini with carbachol abolished the high affinity state of the CCK receptor and converted approximately 25% of the low affinity receptors to the very low affinity state. Carbachol treatment was particularly useful in establishing the values of Kd for the high and low affinity states for different CCK receptor agonists and antagonists. Of the various CCK receptor agonists tested, CCK-8 had the highest affinity for the high affinity state (Kd approximately 1 nM), whereas CCK-JMV-180 had the highest affinity for the low (Kd 7 nM) and very low affinity (Kd 200 nM) states. Gastrin and de(SO4)CCK-8 had affinities for the high and low affinity states of the receptor that were 100- to 400-fold less than those of CCK-8 but had affinities for the very low affinity state that were only 3- to 10-fold less than that of CCK-8. CCK receptor antagonists showed several patterns in interacting with the different states of the CCK receptor. L-364,718 had the same affinity for each state of the CCK receptor. CR1409 and Bt2cGMP each had similar affinities for the high and low affinity states and lower affinity for the very low affinity state. L-365,260 and CCK-JMV-179 had the highest affinity for the low affinity state and lower affinities for the high and very low affinity states. Different CCK receptor agonists caused the same maximal stimulation of amylase secretion but showed different degrees of amplification in terms of the relationship between their abilities to stimulate amylase secretion and their abilities to occupy the low affinity state of the CCK receptor. When amplification was expressed quantitatively as the value of Kd for the low affinity state divided by the corresponding EC50 for stimulating amylase secretion the values were CCK-8 (1000), de(SO)CCK-8 (1500), gastrin (100) and CCK-JMV-180 (Menozzi, D., Vinayek, R., Jensen, R.T. and Gardner, J.D. (1991) J. Biol. Chem. 266, 10385-1091).(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical regulation of the three different states of the cholecystokinin (CCK) receptor in pancreatic acini

We used rat pancreatic acini and measured binding of [125I]CCK-8 and [3H]L-364,718 to the three different states of the CCK receptor to examine potential biochemical regulation of ligand binding for each receptor state. Binding of [125I]CCK-8 to the high affinity state of the receptor was measured as carbachol-inhibitable binding of [125I]CCK-8, whereas binding of [125I]CCK-8 to the low affinity state was measured as carbachol-resistant binding of [125I]CCK-8. Interaction of CCK-8 with the very low affinity state of the CCK receptor was measured as CCK-8-inhibitable binding of [3H]L-364,718. [125I]CCK-8 that was bound to the high affinity state dissociated slowly at a rate of 0.20%/min and this dissociation was not altered by 30 mM NaF. Dissociation of [125I]CCK-8 bound to the low affinity state was biphasic--22% of the bound radioactivity dissociated completely within 3 min and the remaining 78% dissociated slowly at a rate of 0.19%/min. Dissociation of [125I]CCK-8 from the low affinity state was not altered by 30 mM NaF. The pattern of dissociation of bound [125I]CCK-8 from the pancreatic CCK receptor expressed in COS cells was also biphasic and closely resembled that observed in pancreatic acini. CCK-8 that was bound to the very low affinity state dissociated completely during a 20-min period of washing and resuspension of acini that had been first incubated with CCK-8. We found extensive biochemical regulation of the different states of the CCK receptor in pancreatic acini. Bombesin, TPA, NaF, CCCP and trifluoperazine each altered binding of [125I]CCK-8 to the high affinity state and to the low affinity state, and except for bombesin each agent was more potent in affecting the high affinity state than the low affinity state. No agent tested affected the low affinity state but not the high affinity state. In contrast, a number of agents affected the high affinity state but not the low affinity state. These included receptor-mediated agonists (carbachol, secretin, VIP), 8Br-cAMP, NEM, agents that affect microtubules or microfilaments (cytochalasin B, vinblastine), calmodulin inhibitors (W-7, chlorpromazine) and genistein. Experiments with EGTA, A23187 and thapsigargin indicated that none of the three receptor states was influenced by intracellular or extracellular calcium. No agent tested altered the interaction of CCK-8 with the very low affinity state of the CCK receptor.(ABSTRACT TRUNCATED AT 400 WORDS)